The present invention relates to a process for stabilizing the operation of an axial gas laser which includes at least one laser excitation tube and at least one gas circulation system, with connecting devices being provided between the gas circulation system, laser excitation system and axial gas laser.
During the operation of axial gas lasers used, for example, to weld longitudinally extending seams on cans in the canning industry, periodically occurring thickenings can frequently be seen on the welded seam as a result of, for example, a phenomena such as pulsations in the laser power.
The aim underlying the present invention essentially resides in minimizing, if not avoiding, the occurrence of periodically occuring thickening in the longitudinally extending weld seams in cans.
In accordance with advantageous features of the present invention, at least portions of the frequencies of pressure curve frequency components produced by pressure pulsations in the gas circulation system as well as resonant frequencies of the load on the circulation system formed at least by the excitation tube and the connection device or devices may be advantageously selected.
Considering an axial gas laser of this type, one must view the gas circulation system essentially as a source of alternating signals which generates pressure at the output side of the system and, for example, in accordance with a number of compression chambers provided as well as rotational speed of the device, the pressure pulsating around an average pressure value at a basic frequency determining by such parameters. Depending on the construction of the gas circulation system, the initial pressure, with purely sinewave pulsations, has a single frequency component with pulsation which differs from a sinusoidal shape additional frequency components corresponding to higher harmonics.
The excitation tube, connecting devices and any additional devices coupled thereto such as, for example, electrical devices for electrical DC or AC excitation of the excitation tube, combine to form a common frequency dependent load impedance which imposes a load on the gas circulation system as a source. As known, mechanical systems can generally be viewed in complete analogy to electrical impedances and, consequently, mechanical, acoustical, electrical and other mixed systems can be treated in a system by looking toward electro-mechanical analogies.
If the general impedance, viewed by the source as a load, such as a transformer, with a frequency-dependent transformer function as given by a Bode diagram, has resonant frequencies which correspond to the basic or higher harmonics of the source pressure curve, a resonant circuit exists which is excited at the resonant frequency so that oscillations in the laser output power can occur and, which, in turn, can lead to the above-noted variations in the thickness of the welded seam. When a Roots blower is used as the gas circulation system, the same frequency is encountered in the thickness fluctuations at the welded seam as the pulsating fluctuations generated at the output side by the blower used. If at least one piston-type compressor is used as the gas circulation system, including rotary compressors, Roots compressors, and screw compressors, it is proposed that the basic harmonic of the pressure curve produced by the number of compression chambers and rotational speed of the compressor provided should be selected to be much higher than at least portions of the resonant frequencies of the load by increasing the number of chambers and/or the rotational speed, especially the less damped resonant frequencies.
If the individual components of the load, electrical system/gas excitation tube/connecting device, are uncoupled from one another, the resonant frequencies of the partial systems can be considered individually, which is much simpler than an overall examination of the total system. As a result, the laser tube and connecting device can now preferably be uncoupled from one another in terms of frequency, by blowing the gas from the connecting device into the laser tube.
The fact that a buffer volume is also provided on the connecting device for the gas, the volume being much greater than the volume amplitudes of the periodic circulation volume pulsations produced by the gas pressure device, causes the pressure fluctuations to be sharply damped with respect to their effect on the laser tube, the large volume acts as a lowpass element. If such a buffer volume is provided, assurance must be given that when two or more gas supply lines are provided for the laser tube and/or the laser tube arrangement, the gas supply to all supply lines is the same. In addition, the buffer volume is provided in a chamber which is axially parallel to the laser tube, from which n lines with n.gtoreq.2 extending radially to the laser excitation tube and dimensioned so that the cross-sectional area of a chamber A.sub.zu and the line cross-sectional areas L.sub.Lm as well as coefficient of resistance .zeta..sub.Ln have the following relationship: ##EQU1##
Preferably, according to the present invention, the coefficient of resistance .zeta..sub.n is thus increased in the lines n by providing grids, honeycomb structures or the like.
One of the axial gas lasers according to the present invention for achieving the goal desired hereinabove is characterized by the fact that a turbo compressor is provided as a gas circulation system, which turbo compressor generates practically no pressure pulsations on the output side.
It is also possible in accordance with the present invention to provide an axial gas laser with at least one laser excitation tube, at least one gas circulation system and connecting devices between the gas circulation system and the laser excitation tube, with the connecting devices comprising at least one buffer chamber between the circulation system and excitation tube, and with the volume of the at least one buffer chamber being much greater than amplitudes of the circulation volume pulsations caused by the gas circulation system.
It is also possible for the gas circulation system of the present invention to comprise at least one turbo compressor.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings.